1. Field of the Invention
The present invention relates generally to power transmission chains. More particularly, the present invention relates to a chain constructed with unequal pitch lengths which are randomized throughout the chain. The invention has particular application to power transmission chains of the roller chain variety, which are used in engine timing applications as well as industrial applications.
2. Description of the Prior Art
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing drives as well as for the transfer of power from the engine to the transmission or for the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is referred to as "silent chain". Such chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins received in a pair of apertures. An example of silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference.
A second type of chain is know as "roller chain". A typical roller chain consists of alternate inner links and outer links. The inner links, which are also known as "bushing" links, consist of spaced sidebars with bushings tightly received in openings, or apertures, at each end of the sidebars. The outer links, which are also known as "pin" links or guide links, consist of spaced sidebars with pins tightly received in openings, or apertures, at each end of the sidebars. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers are provided on the bushings, and when the roller chain is wrapped about a sprocket, the teeth of the sprocket are received between the laterally spaced sidebars and the longitudinally spaced rollers. An example of roller chain is found in U.S. Pat. No. 4,186,617, which is incorporated herein by reference.
Roller chain drives can include both "true roller" and rollerless design. The true roller design includes the described rollers mounted about the bushings. Rollerless chain contains bushings that directly contact the sprocket teeth. Both types of roller chain are typically specified in industry as British Standard chain and American National Standards Institute (ANSI) chain.
A conventional power transmission drive is comprised of either a silent chain or a roller chain wrapped about at least two sprockets supported by shafts. The chain is endless and assembled from interconnected links that are adaptable to fit over and about teeth formed on the sprockets. Movement of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket may be mounted on the engine crankshaft and the driven sprocket mounted on a valve camshaft. The rotation of the camshaft is thus controlled by the rotation of the crankshaft through the chain.
Noise is associated with such chain drives. Noise is generated by a variety of sources, but in roller chain drives it can be caused by the impact sound generated by the collision of the rollers and the sprocket at the onset of meshing. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket.
The meshing impact sound is generally a periodic sound in chain drives. The impact sound is repeated with a frequency approximately equal to that of the frequency of the chain meshing with the sprocket. The frequency can be related to the number of teeth on the sprocket and the speed of the sprocket. Noise may also be caused, in part, when successive rollers engage the sprocket teeth and then gradually roll or slide into their final positions at the root diameter of the sprocket.
Many efforts have been made to decrease the noise level and pitch frequency distribution in chain drives of both the silent chain and the roller chain variety. The problem of noise reduction in silent chain drives was addressed in U.S. Pat. No. 4,342,560 by changing the contacts between the link flanks of a silent chain and the sprockets by having differently configured link flanks in different sets of the chain. By mixing of links of differing flank configuration, U.S. Pat. No. 4,342,560 attempted to modify the pattern of sound emanating from the chain contacting the sprocket by altering the types of link configurations and thus altering the point and rhythm of contacts. The sets of links of different configurations are placed in random patterns throughout the length of the chain. The resulting chain is often referred to as "hybrid" chain or "random" chain.
Other attempts to alter the rhythm of contacts between the silent chain drive and the sprocket taught the modification of the sprocket teeth. For example, U.S. Pat. No. 3,377,875 and U.S. Pat. No. 3,495,468, teach relief of sprocket teeth in order to achieve noise reduction in contacts between the silent chain and the sprocket.
In the area of side-bar chains for cone pulley transmissions, U.S. Pat. No. 4,344,761 describes a side-bar chain construction which is designed to prevent sympathetic vibrations between the chain and the cone pulleys. The patent teaches causing the lengths of selected links between associated articulation points to differ from those of the remaining links. U.S. Pat. No. 4,650,445 discusses various other methods of construction of silent chains and chain-belts for variable pulley transmissions that are attempts to modify the generated noise pattern.
The present invention utilizes these generic concepts of noise reduction in a roller chain. The present invention seeks to provide a roller chain construction that modifies the pattern of chain and sprocket contacts through the use of unequal pitch lengths in the chain. These unequal pitch lengths are achieved through the use of varying link lengths; rollers and bushings of differing sizes and configurations; and varying sprocket tooth spacing.